[2.0] WebPages in C#

I am working on a Windows Application in C# using VS 2005

In my application when I click the Show Salary button from a MenuBar
It adds a new Tab Page called Salary and updates the Salary Info.

I have two text boxes which takes the name.

I am using Event Handlers to handle the events.

Question:

When I click the Show Salary from the menu. Everything works fine, the Salary information is updated.

But when I change the person's name and click on the Lookup Button.

Error:
System.InvalidCastException was unhandled
Message="Unable to cast object of type 'System.Windows.Forms.Button' to type 'System.Windows.Forms.TabPage'."
Source="WindowsApplication1"
StackTrace:
at WindowsApplication1.Form1.UpdateSalaryTabPage(Object sender, EventArgs e) in C:\Documents and Settings\sramakrishna\My Documents\Visual Studio 2005\Projects\WindowsApplication1\WindowsApplication1\Form1.cs:line 175
at System.EventHandler.Invoke(Object sender, EventArgs e)
at System.Windows.Forms.Control.OnClick(EventArgs e)
at System.Windows.Forms.Button.OnClick(EventArgs e)
at System.Windows.Forms.Button.OnMouseUp(MouseEventArgs mevent)
at System.Windows.Forms.Control.WmMouseUp(Message& m, MouseButtons button, Int32 clicks)
at System.Windows.Forms.Control.WndProc(Message& m)
at System.Windows.Forms.ButtonBase.WndProc(Message& m)
at System.Windows.Forms.Button.WndProc(Message& m)
at System.Windows.Forms.Control.ControlNativeWindow.OnMessage(Message& m)
at System.Windows.Forms.Control.ControlNativeWindow.WndProc(Message& m)
at System.Windows.Forms.NativeWindow.DebuggableCallback(IntPtr hWnd, Int32 msg, IntPtr wparam, IntPtr lparam)
at System.Windows.Forms.UnsafeNativeMethods.DispatchMessageW(MSG& msg)
at System.Windows.Forms.Application.ComponentManager.System.Windows.Forms.UnsafeNativeMethods.IMsoCompo nentManager.FPushMessageLoop(Int32 dwComponentID, Int32 reason, Int32 pvLoopData)
at System.Windows.Forms.Application.ThreadContext.RunMessageLoopInner(Int32 reason, ApplicationContext context)
at System.Windows.Forms.Application.ThreadContext.RunMessageLoop(Int32 reason, ApplicationContext context)
at System.Windows.Forms.Application.Run(Form mainForm)
at WindowsApplication1.Program.Main() in C:\Documents and Settings\sramakrishna\My Documents\Visual Studio 2005\Projects\WindowsApplication1\WindowsApplication1\Program.cs:line 17
at System.AppDomain.nExecuteAssembly(Assembly assembly, String[] args)
at System.AppDomain.ExecuteAssembly(String assemblyFile, Evidence assemblySecurity, String[] args)
at Microsoft.VisualStudio.HostingProcess.HostProc.RunUsersAssembly()
at System.Threading.ThreadHelper.ThreadStart_Context(Object state)
at System.Threading.ExecutionContext.Run(ExecutionContext executionContext, ContextCallback callback, Object state)
at System.Threading.ThreadHelper.ThreadStart()

This is my code:

-----------------------------------

using System;
using System.Collections.Generic;
using System.ComponentModel;
using System.Data;
using System.Drawing;
using System.Text;
using System.Windows.Forms;

namespace WindowsApplication1
{
public partial class Form1 : Form
{
private Employees employees;
private Employee employee;
//TabPage tabpg;
public Form1()
{
InitializeComponent();
}

private void Form1_Load(object sender, EventArgs e)
{
//hookup common validation event handler for text boxes:
this.txtFirstName.Validating += new CancelEventHandler(this.nonEmpty_Validating);
this.txtLastName.Validating += new CancelEventHandler(this.nonEmpty_Validating);

/* hookup event handlers for Lookup click, which also triggers updates of common tab pages
**
** NOTE: order here is important, since called in this order --- and we want cmdLookup to run first & do
** the lookup before we start updating the tab pages.
*/

this.btnLookUp.Click += new EventHandler(this.btnLookUp_Click);
this.btnLookUp.Click += new EventHandler(this.UpdateContactInfoTabPage );
this.btnLookUp.Click += new EventHandler(this.UpdateHomeAddrTabPage);

this.employees = new Employees();

}
//General validation method for textboxes that require a non-empty string.
private void nonEmpty_Validating(object sender, System.ComponentModel.CancelEventArgs e)
{
TextBox txt;
txt = ((TextBox)(sender));
if (txt.Text == string.Empty )
{
MessageBox.Show("Please enter a value...");
e.Cancel = true;
return;
}

}

private void exitToolStripMenuItem_Click(object sender, EventArgs e)
{
this.Close();
}

//
//Called to dynamically show/hide the "Salary" tab page
//
private void showSalaryToolStripMenuItem_Click(object sender, EventArgs e)
{

if (this.showSalaryToolStripMenuItem.Text.StartsWith("Show"))
{
//Show Salary tab, which we create on the fly
//
TabPage tabpg;
tabpg = new TabPage("Salary");
tabpg.Name = "tabpgSalary";
tabpg.ForeColor = Color.Red;

Label lbl;
lbl = new Label();
lbl.Text = "Salary:";
lbl.Location = new Point(30, 40);

TextBox txt;
txt = new TextBox();
txt.Name = "txtSalary";
txt.Location = new Point(100, 37);
txt.ReadOnly = true;
txt.Size = new Size(200, 26);

tabpg.Controls.Add(txt);
tabpg.Controls.Add(lbl);

this.tabctrlEmployeeInfo.TabPages.Add(tabpg);
if (this.employee != null)
{
//we have an employee being displayed, show their salary
txt.DataBindings.Add("Text", this.employee, "FormattedSalary");
}

this.showSalaryToolStripMenuItem.Text = "Hide Salary"; //flip menu text
//now that tab is visible, add event handler to update when a lookup is performed
this.btnLookUp.Click += new EventHandler(this.UpdateSalaryTabPage);
// but update tab to reflect any lookup we've already done
//this.UpdateSalaryTabPage(null, null);
}
else
{
//
//Hide Salary tab by discarding what we created earlier...
//
this.tabctrlEmployeeInfo.TabPages.RemoveAt(2);
this.showSalaryToolStripMenuItem.Text = "Show Salary"; //flip menu text

//remove event handler to update tab page since page is now gone!
this.btnLookUp.Click -= new EventHandler(this.UpdateSalaryTabPage);
}

}

/**
** These methods are triggered when the user looks up an employee, which will in turn require updates
** on the various tab pages
**/
private void btnLookUp_Click(object sender, EventArgs e)
{

//Lookup new Employees...
this.employee = this.employees.Lookup(this.txtFirstName.Text, this.txtLastName.Text);

//If found, display his/her info, otherwise display an error message...
if (this.employee == null)
{

MessageBox.Show("Employee not found...");
this.txtFirstName.SelectAll();
this.txtFirstName.Focus();
}
else
{
//** nothing, updates are triggered as part of event processing...
}
}

private void UpdateContactInfoTabPage(object sender, System.EventArgs e)
{
this.txtEmail.DataBindings.Clear();
this.txtEmail.Clear();
this.txtCellPhone.DataBindings.Clear();
this.txtCellPhone.Clear();
if (this.employee == null)
{
return;
}
this.txtEmail.DataBindings.Add("Text", this.employee, "Email");
this.txtCellPhone.DataBindings.Add("Text", this.employee, "CellPhone");
}

private void UpdateHomeAddrTabPage(object sender, System.EventArgs e)
{
this.txtCity.DataBindings.Clear();
this.txtCity.Clear();
this.txtState.DataBindings.Clear();
this.txtState.Clear();
if (this.employee == null)
{
return;
}
this.txtCity.DataBindings.Add("Text", this.employee, "City");
this.txtState.DataBindings.Add("Text", this.employee, "State");
}

private void UpdateSalaryTabPage(object sender, System.EventArgs e)
{
TabPage tabpg = (TabPage) sender ;
this.tabctrlEmployeeInfo.TabPages["tabpgSalary"].Equals(tabpg);
tabpg.Controls["txtSalary"].DataBindings.Clear();
((TextBox)(tabpg.Controls["txtSalary"])).Clear();
if (this.employee == null)
{
return;
}
tabpg.Controls["txtSalary"].DataBindings.Add("Text", this.employee, "FormattedSalary");
}

}
}
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